1. Field of the Invention
The present invention relates to a source driver and a data switching circuit thereof, and more particularly, to a source driver using a dot inversion driving method and a data switching circuit thereof.
2. Description of the Related Art
The source driver is a key component in the Thin Film Transistor Liquid Crystal Display (TFT LCD) for converting a digital data signal required for displaying image into an analog signal, and providing the analog signal to each sub-pixel (also known as a dot) of the TFT LCD.
FIG. 1 is a block diagram illustrating the major structures of a conventional source driver 100. Referring to FIG. 1, the source driver 100 receives a data signal 110 and outputs the analog signals from its N output channels Y1˜YN. The source driver 100 includes a shift register 101, a line latch 102, a level shifter 103, a digital-to-analog converter (DAC) 104, and an output buffer 105. In general, the source driver is a conventional art and its structures and functions are apparent to one of the ordinary skill in the art. The process is briefly described below. First, a data signal 110 is dispatched by the shift register 101 and output to output channels Y1˜YN. Then, the output from the output channels Y1˜YN are temporarily stored in the line latch 102 and then amplified by the level shifter 103. Finally, the DAC 104 converts the amplified data signals into analog signals, which are then outputted by the output buffer 105.
Since the TFT LCD uses liquid crystal for controlling the display, the TFT LCD must be driven by an alternating current (AC) to avoid the liquid crystal material from being polarized. Accordingly, a variety of inversion driving methods, such as line inversion, column inversion, and dot inversion are developed. Wherein, the dot inversion driving method is shown in FIG. 2. FIG. 2 schematically shows the driving polarity of the sub-pixel in TFT LCD in a frame T and the next frame T+1, where “+” represents a positive driving polarity, and “−” represents a negative driving polarity. As shown in FIG. 2, the so-called dot inversion means that both neighboring sub-pixels in the same frame have opposite driving polarities in their horizontal and vertical directions, and the driving polarity of the same sub-pixel will be inversed as it goes to the next frame.
Although the dot inversion driving method has many advantages, its major disadvantage is the consumption of excessive power. Referring to FIG. 3, the source driver 301 in FIG. 3 outputs the analog signals to the sub-pixels SP0˜SP3 located on the same scan line in a pixel array 303 through the output buffer 302 and the data lines DL0˜DL3. The largerscreen TFT LCD panel in current market adopts the direct current (DC) common voltage Vcom design, and having a positive polarity voltage and a negative polarity voltage. Wherein, the positive polarity voltage is higher than the common voltage Vcom, and the negative polarity voltage is lower than the common voltage Vcom. For example, the sequence of the voltage polarity output from the data lines DL0 and DL2 is positive, negative, and positive; and the sequence of the voltage polarity output from the data lines DL1 and DL3 is negative, positive, and negative. Each time as it enters into the next scan line or the next frame, the polarity of the voltage on the data lines DL0˜DL3 must be inversed. Therefore, the source driver 310 should provide a swing voltage Vswing that is twice of the common voltage Vcom. The greater the swing voltage Vswing is, the greater the power is consumed. Along with the increasing of panel size and the resolution, a higher voltage is required to drive the wide view angle technology such as the in-plane switching (IPS) and the multi-domain vertical alignment (MVA). As a result, the problem is made more serious.